349 Intersection of Two Arrays

Given two arrays, write a function to compute their intersection.

Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].

Note: Each element in the result must be unique. The result can be in any order.

The Idea: The intersection of two arrays are the elements they have in common.

Complexity: O(N) time and space

vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
    unordered_set<int> s(nums2.begin(), nums2.end());

    vector<int> intersect;

    for (auto i : nums1) {
        if (s.find(i) != s.end()) {

    return intersect;


class Solution:
    def intersection(self, nums1, nums2):
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        if not nums1 or not nums2:
            return []
        return list(set(nums1) & set(nums2))

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